The present invention relates to liquid crystal display (LCD) devices, and more specifically, to the prevention or elimination of non-uniformity in a display due to the non-uniformity of the thickness of liquid crystal cells employed in color LCD devices.
In a conventional (color) liquid crystal display device 120 (commonly referred to as an LCD device, LCD unit or sometimes just LCD), as is shown in FIGS. 8 and 9, an active matrix thin film transistor (TFT) array substrate 1 and a common electrode substrate 2 are disposed in close proximity to each other in an opposing manner. A liquid crystal layer 3 fills the space between them. On the TFT array substrate 1, source bus 6, which preferably forms vertical columns, and gate bus 7, which preferably forms horizontal lines, preferably intersect each other, forming a net-like meshed pattern. The protruding surfaces of the source bus 6 and the gate bus 7 (referred to hereafter as both buses) are preferably disposed approximately on the same plane. Picture element electrodes 8 within the meshes made by both buses are preferably formed to be considerably thinner than both buses, and a TFT 9 is preferably formed corresponding to the picture element electrode 8 on the periphery of each mesh (as also illustrated in FIG. 11).
When a gate voltage for scanning is applied to the gate bus 7, the TFT 9 is turned on, and the charge from the image signal applied to the source bus 6 is stored in the picture element capacity formed between the picture element electrode 8 and the common electrode 16 below.
As illustrated in FIGS. 8-12, in order to increase the conductivity of the source bus 6 of conventional liquid crystal display (LCD) device 120, the source bus 6 is preferably formed as a three-layer construction, and preferably, of indium tin oxide (ITO) 6a, molybdenum (Mo) 6b, and aluminum (Al) 6c. A protruding surface of source bus 6 is preferably formed approximately to the same height as a protruding surface of the gate bus 7. At the places where both buses 6 and 7 intersect, as is shown in FIG. 12, the source bus 6 is preferably made thin. In other words, a groove is cut in source bus 6. On top of source bus 6 is preferably formed an insulating film (SiNx) 11, and thereafter, the gate bus 7 is preferably formed in such a way that at points of intersection, the overall formation does not get particularly high or thick. Thus, as can be seen from FIG. 12, a gap is formed between both buses. Thus, buses 6 and 7 do not make electrical contact with each other where they cross or intersect.
Referring to FIG. 9, a black matrix 14 preferably forms a net-like pattern on a glass substrate 13 of a common electrode substrate 2. The net-like pattern (meshes) of black matrix 14 preferably opposes the meshes of TFT array substrate 1. In the meshes of the black matrix 14, red R, green G, and blue B color filters 15 are preferably formed, each filter being separated from adjacent filters by a gap. Common electrode 16 is preferably formed on the inner surface of the glass substrate 13 on which the color filters are formed. Common electrode 16 is preferably formed in such a way that it covers the entire surface.
There are various types of color filters known in the art for conventional CD device 120. Typically, for color filters 15, filters with differing thicknesses for R, G, B colors are preferably used. With color filters 15, the intensity of the transmitted light of the liquid crystal cells differs according to the R, G, and B wavelength. In order to compensate for this, the thicknesses for the each of the R, G, B color filters are preferably different. Typically, the thicknesses t for the color filters R, G, and B, identified as tr, tg, and tb (as seen in FIG. 9), are preferably such that tb greater than tg greater than tr. As a result, an LCD device which employs these filters has liquid crystal cells, each cell varying in thicknesses due to the use of R, G, and B filters. The formation of filters with different thicknesses within an LCD device is known as multigap construction.
In conventional LCD devices 120, display non-uniformity results from, among other factors, non-uniformity in the thicknesses of the liquid crystal cells. When display non-uniformity occurs, visibility diminishes. For this reason, before the two substrates 1 and 2 are joined together in the LCD, granular spacers (not shown) with the same diameter are preferably spread uniformly on the TFT array substrate 1 and the common electrode substrate 2. Thereafter substrates 1 and 2 are joined together and the liquid crystal is inserted. The thickness of the cells is determined by the spacers employed.
However, with a multigap color LCD (which has color filters, preferably R, G and B, of varying thickness which are not equal to each other), the uniformly spread spacers do not function effectively in properly setting the thickness of all the liquid crystal cells. For example, referring to FIGS. 11 and 12, on the common electrode substrate 2, a blue color filter 15b is formed thicker than a red color filter 15r, and a green color filter 15g, with the top of the blue color filter 15b protruding the most. As a result, in the regions where the blue color filter 15b overlaps with both buses 6 and 7, namely, the shaded areas in FIG. 8, the distance between the formations on substrates 1 and 2 (referred to as cell thickness d), is thinnest, and both glass substrates 1 and 2 are supported only by the spacers spread in this region. As those of skill in the art of conventional LCD devices 120 will recognize, the shaded regions as illustrated in FIG. 8 depict the portions where the spacers are effective to prevent display non-uniformity, yet make up only a small portion of the surface area of substrates 1 and 2. Because spacers have a tendency to move, if this effective region is small, the cell thickness is not always stable. In this situation, non-uniformity in cell thickness occurs, thereby causing non-uniformity in display. Accordingly, it is one of the objects of the present invention to make the effective region of spacers within the liquid crystal larger, keep cell thickness stable, eliminate non-uniformity of cell thickness and prevent non-uniformity of the color LCD display.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can only be gained by considering the entire specification, claims, and drawings, as a whole.
The present invention is a multigap liquid crystal display having a thin film transistor (TFT) array substrate and a common electrode substrate formed together. The tallest color filters (preferably blue color filters) are formed so that their surface area does not overlap the source bus and the gate bus surrounding the opposing picture element electrodes above. In addition, the shorter (preferably green) color filters are formed to overlap the source bus and the gate bus surrounding the opposing picture element electrodes above. Furthermore, the film thickness of the source bus, the gate bus, the taller (preferably blue) color filter thickness tb and the shorter (preferably green) color filter thickness tg are set so that the distance between the shorter (preferably green) color filters and both buses is set approximately equal to the distance between the taller (preferably blue) color filters and the picture element electrodes.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the spirit and scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.